The present invention generally relates to network monitoring and more particularly to verifying connectivity and detecting defects between monitoring points within a network.
Transport networks are used today to provide connectivity services to other networks. For example, transport networks may provide service links, connections, or form subnetworks that become part of the topology of a larger network. The topology of a network is generally static to support stable network operation and predictable performance across the network. Thus, transport services may have long holding times and it may become necessary to continuously monitor the transport services in order to ensure that the transport services continuously provide an agreed connectivity and performance. Traditionally, transport networks have been maintained over “connection oriented” networks, in which reference points are dedicated and exclusive to a communication link between one sender point and one receiver point. In a connection oriented network, the relationship between a sender point and receiver point is set up a priori. Methods exist for monitoring connection oriented networks in order to establish and provide means to detect a variety of defects in a connection, for example, misconnection, disconnection, bit error rate, etc.
However, more recently, connectionless networking technologies have been considered for providing transport services. Connectionless networks do not maintain exclusive communications links between reference points within the network. Examples of connectionless networking technologies are IP (Internet Protocol), Ethernet, CLNP (Connectionless Network Protocol), IPX (Internetwork Packet Exchange), DECnet, AppleTalk, token bus, token ring and FDDI (Fiber Distributed Data Interface). Connectionless transport services differ from connection oriented services primarily in that the reference points in a connectionless network are not exclusive to a communication link between one sender point and one receiver point. Instead, in a connectionless network, the relationship between a sender point and receiver point need not be set up a priori.
In connectionless networks, the receiver points at a boundary of the transport service may carry traffic from multiple sender points. In addition, the sender points at the boundary may transmit traffic to multiple receiver points. Thus, there are no identifiable exclusive connections to monitor. Therefore, conventional methods that are designed to monitor connection oriented networks are not easily applied to connectionless network monitoring.
Furthermore, connectionless transport services generally provide a connectionless subnetwork that affords connectivity among multiple points at the boundary of the subnetwork. In many cases multiple transport services may be supported on a single physical network infrastructure. When multiple transport services are supported on a common infrastructure, the underlying network resources are partitioned between the transport services. For example, the network services may be partitioned between separate transport services to form a virtual network or network fragment.
However, defects that may arise with virtual networks or network fragments are different from those that may occur with a connection oriented network. A network fragment is defined by the set of boundary points which are allowed to exchange information in the context of the transport service. Examples of defects that may be experienced by network fragments are split network fragments, loss of connectivity to a member or point in the network, mis-joined network fragments and invalid members or points participating in a network fragment. A split network fragment may arise when disjoint subsets of a network fragment exist. A disjoint network fragment subset occurs when points at the boundary of a network fragment experience connectivity with other non-boundary points or members within the network fragment, yet the boundary points have lost connectivity with one another. A boundary point in a network fragment exhibits a loss of connectivity when the boundary point is no longer connected to non-boundary points within the network fragment. A mis-joined network fragment arises when connectivity exists between two or more network fragments that should not be connected to one another (e.g. able to exchange information). An invalid member exists within a network fragment when a boundary point, that is not a member of a network fragment, experiences connectivity to other points that are members of the network fragment.
Presently, standards are being defined regarding operation, administration and maintenance (OAM) functions for connectionless transport services, such as for Ethernet and IP in order to detect various defects in these networks and network fragments (e.g. virtual private networks). Current IP standards do not explicitly address detection of defects for connectionless network fragments. Further, draft Ethernet standards are being proposed regarding detection of certain types of defects; however, the mechanisms proposed thus far are complex and not easily scaled to large networks.
By way of example, one proposal for Ethernet OAM requires each monitoring point in a network fragment to multicast an OAM message to all other monitoring points. Multicasting the OAM message involves broadcasting the OAM message throughout an entire Ethernet fragment. Consequently, each monitoring point must receive and process the OAM messages from all other monitoring points within the network fragment.
FIG. 1 illustrates an conventional network 100 that is configured to verify network connectivity through multicasting OAM or monitoring messages between monitoring points 101-107. The monitoring messages that are sent from monitoring point 102 are shown by solid arrows, while the monitoring messages that are received by monitoring point 102 are shown by dashed arrows. When utilizing the multicasting monitoring method of the network 100, in an N-point network fragment, each monitoring point must regularly receive monitoring messages from N−1 sender points, process monitoring messages from N−1 sender points, and maintain connectivity states with respect to N−1 sender points. For example, monitoring point 102 receives and processes monitoring messages from monitoring points 101, 107, 106, 105, 104 and 103. In addition, monitoring point 102 must also maintain connectivity states with respect to each of the monitoring points 101, 107, 106, 105, 104 and 103. Thus, the monitoring process implemented by network 100 places a large processing burden on each monitoring point for a network fragment having a large number of monitoring points.
Furthermore, the monitoring process implemented by network 100 incurs a large provisioning burden when a monitoring point is added to or removed from the network fragment. When a monitoring point is added to the network fragment, all other monitoring points must be informed (provisioned) of the change and instructed to expect (or no longer expect) monitoring messages from the added/removed monitoring point. Adding and removing monitoring points from a large network fragment introduces a large provisioning burden upon the network.
Also, the network 100 is unable to detect defects in unicast message forwarding between boundary points through the multicast monitoring message. The inability to detect defects in unicast message forwarding is due to the fact that the monitoring process of the network 100 utilizes a multicast address to send monitoring messages between boundary points. When a defect exists within a unicast forwarding process between boundary points, the conventional monitoring method is unable to isolate and recognize the defect. Instead, the conventional network 100 must separately test each unicast forwarding process between individual pairs of boundary points in addition to multicast monitoring. However, it is burdensome to test unicast forwarding between all pairs of boundary points in a large network fragment.
Finally, the use of a multicast address to send monitoring messages is problematic when different administrative entities want to monitor nested domains or areas of a network or network fragment. To enable different administrative entities to monitor multiple domains or areas, a mechanism must be provided to distinguish monitoring messages that are associated with the different administrative entities, in order to ensure monitoring messages are forwarded or captured appropriately, and to detect and handle leakage of monitoring messages outside of the intended administrative domain or area. This is similar to the “tandem connection monitoring” problem in connection oriented networks, in which a sub connection of a larger connection is to be monitored independently of the monitoring of the larger connection. In accordance with one current proposal, eight “monitoring levels” are defined. The use of multiple monitoring levels requires each monitoring point to recognize and filter monitoring messages based on the monitoring level indicated in the monitoring message. The addition of monitoring levels and the associated processing rules adds significant complexity to the monitoring mechanism.
A need remains for improved systems and methods of verifying connectivity and detecting defects between monitor points within a network.